The present invention relates to a heat-treating apparatus provided with an interlock function for a maintenance door of a load lock chamber, and a treating gas exhaust duct.
In general, in apparatus such as oxidation dispersal apparatus and other apparatus for the heat-treating of semiconductor wafers, the oxidation dispersal reaction is performed in a high temperature status of 1200.degree. C. for example, when compared to film growth processing by the CVD method. Because of this, when metal materials are used in the furnace portion of the heat treating furnace, metallic contamination of the semiconductor wafers may occur and when a corrosive gas is used as the treating gas, the metallic members that configure the interior of the furnace are corroded and the products formed are dispersed and attach to the surface of the semiconductor wafer, so that there is also the danger of their performance deteriorating. It is because of this that the treating vessel of a heat-treating furnace is configured of glass or some substance that has corrosion resistance and heat resistance. A tube for the introduction of the treating gas to the treating vessel of the heat-treating furnace and a tube for the exhaust of the gas after treatment are made of glass, and are mounted to form a unit with the heat-treating apparatus itself in a configuration where steam or the like is supplied to inside the treating vessel and oxidation dispersion treating for the semiconductor wafer is performed at normal pressure and in a high-temperature status of 200.degree. C. for example.
Recent high integration of LSI such as the improved mounting density of MOSFET for example, has led to recent LSI such as 1.4M DRAM for example, having a minimum design width of 1 .mu.m or less, and for the film thickness of the gate oxide film being 200 .ANG. or less. Also, the gate oxide films of 16M DRAM are also tending to be thinner than 100-150 .ANG..
When the pre-processing prior to the film formation of the semiconductor wafer involves wetting and cleaning the silicon surface by HF (hydrofluoric acid) and HCl (hydrochloric acid), there is a clean silicon surface on the semiconductor wafer after cleaning but the oxygen and water components in the atmosphere soon react with the silicon to form a natural oxidation film about 10 .ANG. thick on the surface.
In addition, when there is a lateral type of heat-treating furnace, the boats mount the semiconductor wafers mounted to them are driven in the horizontal direction into a reaction vessel that has been heated to 1000.degree. C. for example and are loaded, and there is the possibility that an opposing air flow caused by the temperature difference between the inside and the outside of the furnace may cause air to enter into the reaction vessel of the heat-treating apparatus. Because of this, when there is a lateral type of furnace, it is not possible to avoid the heated wafer reacting with the oxygen in the air when there is loading, and a natural oxidation film of 50-100 .ANG. thick forming on the surface of the water. Also, since this natural oxidation film is porous and has a poor film quality, there is a limit to application to the high density elements for which control of the gate oxide film is necessary.
On the other hand, when a vertical type of heat-treating furnace is used, there is little intake of oxygen to inside the reaction vessel when compared to the case for the horizontal type of furnace and the thickness of the natural oxidation film formed is small at 30-50 .ANG.. Because of this, vertical type heat-treating furnaces are mainly used for film growth in semiconductor wafers for 1M DRAM.
However, with high densities of 4M and 16M for LSI, air is also taken in when there is loading and unloading to and from the furnaces used, and this, and the moisture component absorbed by the wafer cause the formation of a natural oxide film for which improved control is necessary. In particular, with increasingly high densities for semiconductor elements, control of the film thickness of the oxide film, control of the generation of the natural oxide film of around 10 .ANG. and which is formed by the reaction between silicon and the water and oxygen in the atmosphere during the time after the wafer has been cleaned and when it is being transported to the heat-treating furnace, and the exclusion of oxygen and the residual water component inside the heat-treating furnace and that becomes the cause of the formation of the natural oxidation film are essential.
In addition, semiconductor wafer processing apparatus other than apparatus for the formation of oxide films also require control of the generation of excessive natural oxidation films when there is the formation of capacitance films and polysilicon films that require particularly small contact resistances.
The present invention has as an object the effective elimination of these problems and the provision of a heat-treating apparatus that can control the formation of natural oxidation films on semiconductor wafers when there is wafer loading to a heat-treating apparatus.
Also, in general, for vertical type heat-treating apparatus there has been proposed (such as in "Electronic Materials" (Denshi Zairyo) March, 1989; pages 38, 39) a load lock method that uses a configuration for the airtight control of the atmosphere when the semiconductor wafers are loaded to the furnace.
The conventional load lock method that is disclosed here has a boat raising and lowering mechanism and the like arranged at the bottom of a vertical type of heat-treating furnace, arranged inside a load lock chamber, and after the inside of the chamber has been made a vacuum, an inert gas such as nitrogen or the like is completely filled into the chamber. The loading of the boat to inside the furnace is performed after this. As a result, the natural oxidation of the surface of the wafer is prevented when there is loading, and the formation of natural oxidation films is strongly controlled.
In a load lock chamber of a vertical type of heat-treating furnace such as described above, it is necessary to perform maintenance of the boat raising and lowering mechanism that is housed inside it, or to clean the film that has adhered to the wafer boat for example, and so the maintenance door to the load lock chamber must be opened and closed comparatively frequently. In this case, the workers must enter the chamber in order to perform work to take the lowered wafer boat for example, to outside of the chamber. However, as has been described above, the inside of the chamber is filled to normal pressure with nitrogen or some inert gas, and in a worst case, entering the chamber could result in asphyxiation of the worker.
Not only this, even in cases where a worker stands near the door leading to the chamber but does not enter the chamber, the worker is nevertheless enveloped in a large amount of nitrogen gas when the maintenance door is opened. In addition, the capacity of the chamber is tending to become larger in order to house wafer boards for which the diameter is increasing to 8 inches or more, and for which the batch processing number per time is also increasing. This means that the problem described above must be solved all the more urgently.
In the light of the problem described above, the present invention is proposed for the effective elimination of the problem described above, and has as an object the provision of an interlock mechanism that releases the lock of the maintenance door of the chamber after the gas filled inside the load lock has been replaced by air and the oxygen concentration has attained a required value.